The invention relates to a transparent heat protection element comprising at least one carrier element and one protection layer comprising hydrous alkali silicate as well as a process for the fabrication of heat protection elements.
Transparent heat protection elements of this type are known in various implementations and are used inter alia as structural elements. Glass plates most frequently serve as carrier elements, however, other transparent. materials can also be used such as, for example, synthetic materials. Especially high requirements are made of the heat protection of structural elements which, in the form of glazing, form boundaries of rooms or are used for doors. From DE C3 19 00 054, heat insulating transparent laminated glasses are known, in which a layer comprising dried hydrous alkali silicate is disposed between two glass surfaces. Under the influence of heat on this laminated glass, for example in the event of fire, the intermediate layer comprising alkali silicate foams and the water contained in the alkali silicate vaporizes. In this way the intermediate layer becomes impermeable to heat radiation and for a given length of time, forms effective protection against undesired heat transmission. Although at least one of the glass plates cracks and breaks, the glass parts adhere to the expanded foam layer. To improve heat protection, several glass plates and intermediate layers comprising alkali silicate are disposed one behind the other. In the fabrication of laminated glasses of this type, a thin layer of alkali silicate is applied in liquid form on one side of a glass plate, and this layer is subsequently dried by drawing off the excess water, for example, through the effect of heat. This drying process is expensive and requires a particular drying time whereby the fabrication process is delayed. The second glass plate must subsequently be affixed by adhesion on the intermediate or protective layer comprising alkali silicate. The manufacture of laminated glasses of this type places high demands on production in order to ensure that no opaqueness of the laminated glass due to the presence of air bubbles or other production defects, occur.
It is further known from EP A-2 192 249, to introduce the alkali silicate of the intermediate layer in the form of a hydrogel layer with increased water content. These hydrogel layers have a water content of 80 to 90% and are therefore not self-supporting. Hydrogel layers of this type are suggested in order to improve the optical properties of the intermediate layer. Since the hydrogel layer itself does not have sufficient cohesion or sufficient adhesion relative to the adjoining glass layers, it is suggested to add an organic binding agent for stabilizing the layer, for example gum arabic. Adding these binding agents is necessary in order to prevent the hydrogel from running out of the interspace between the laminated glasses or in the event one of the glass plates breaks. The disadvantages of the insufficient cohesion and adhesion of the hydrogel layer require additional expensive measures. The content of silicon dioxide is maximally 20 percent by weight and the molar ratio of silicon dioxide and sodium oxide as the alkali metal oxide, ranges from 2 to maximally 4.